Why isn't WebM video supported out of the box in Ubuntu?

http://askubuntu.com –
Ubuntu can't include non-free codecs, but has had the ability to play Ogg Theora and Vorbis files out-of-the-box for years because they're open source. Now that WebM is such a popular, free alternative to H.264, why isn't support included by default?
(HowTos)